出自宋朝祝穆的《方舆胜览·眉州·磨针溪》，只要有恒心，有毅力，持续不断地坚持下去，再难的事也能做成功。
This phrase comes from Zhu Mu’s Song Dynasty work “Phenomenal Observations of Territories – Meizhou’s Needle Grinding Stream.” It means that with perseverance and sustained effort, even the most difficult tasks can be accomplished.
李白小的时候很贪玩，不肯用功读书。
When Li Bai was young, he loved to play and was unwilling to study diligently.
一天，李白书还没有读完就出去玩了。他来到一条小溪边，看到清澈透明的溪水就想下水去玩。突然，一阵磨东西的声音传入他耳中，他抬头四顾，发现不远处有一个老妇人，手里拿着一个大铁棒，在磨刀石上不停地磨来磨去。
One day, Li Bai left his studies unfinished to go play outside. He came upon a small stream and, captivated by the clear flowing water, wanted to go in and play. Suddenly, he heard the sound of something being ground and looked around to see an old woman in the distance holding a large iron pestle, continuously grinding it against a whetstone.
李白觉得很奇怪，就走过去问老妇人说：“老婆婆，您磨这根大铁棒有什么用呢？”
Puzzled, Li Bai approached and asked: “Granny, what are you using that big iron pestle for?”
老妇人抬头看了一眼幼小的李白，说道：“我要把它磨成一根绣花针。”
The old woman looked up at the young Li Bai and replied: “I’m grinding it into a needle for embroidery.”
李白又问：“这根铁棒这么粗，要磨到什么时候才能磨成一根绣花针呢？”
Li Bai asked further: “This pestle is so thick, how long will you have to grind before it becomes an embroidery needle?”
李妇人笑了笑说：“只要功夫深，铁杵就能磨成绣花针！”
The woman smiled and said: “As long as the effort is deep, even an iron pestle can be ground into a needle!”
李白听后，似乎明白了一些道理，于是就辞别老妇人，回家继续读书去了。
After hearing this, Li Bai seemed to understand a principle. He bid the old woman farewell and returned home to continue his studies diligently.